Hi guys,

Can anyone tell me about what are the things i have to consider for taking the vibration readings from an overhung crane?

We have 2 overhung cranes for moving the laddle from the furnace in our steel plant. In one of the crane, there was some failures on some electronic components frequently and a team was formed to investigate. They want to take the vibration measurements of the panel in which the electronic components are fixed and from the door of the cabin. Is it possible to take vibration with a normal accelerometer? What type of setup i have to use for this application? Please feel free to comment on this!!

Have a nice day!!

First though is to establish resonant frequencies of where the board are effected causing them to crack or deteriorate. Amplitude analysis may be of little use??? Are you in Al-jubail? I was at the Jubail complex last in 1996. I was with the Al-Kalifa family then. You may be looking at low frequency stuff??? I'm unsure of the best approach but would consider a sesmeic type transducer and might not rule out an eddy current reading if mounted from a solid wall or I could be way off. It would take more info than presently available.

Jenish,
Do you have an understanding of the type of failures? Loosened board components, cracked circuit boards, loosened or broken connectors, frayed or broken cables/wires? The type of failure can influence the type of vibration measurements and locations. You can start by measuring vibrations on the cabinet corners with a standard accelerometer. Be carefull of light weight surfaces, since accelerometer may be too heavy and alter the measurements. A tiny accelerometer would be needed for mounting on circuit boards, if needed. You may have to measure throughout a full process cycle to identify transient events or worst-case continuous vibrations. A portable data collector may not be suitable for this task, but you can start with it. A multichannel continuous recorder (analog tape, digital tape, or PC-based A/D system)would be ideal for this task.

Walt

You have to ask the question: is there a basic design flaw? Can you design out the problem rather than just monitor it. Maybe RCA is in order.

Sam,

You can do RCA (hypothetical postulating) all you want, but vibration measurements are very usefull. If the vibration environment is excessive for the type and design of the control components, then vibrations can be placed on the short list of possible causes of failures. My only caution to Jenish is to understand the "why and what" of the failures to serve as a guide to making intelligent/usefull measurements.

Walt

Walt, you are right and this analytical should be used in problem solving and RCA. But my response to Jenish is basically, I don't think PdM monitoring of panels is something that is normally done. Why bother, fix the problem and move on. I don't see it as cost justifible to monitor electrical panels or I could be wrong.

Gee Sam, I thought Jenish just wanted to solve a problem with diagnostic measurements and not conduct routine PDM monitoring of the electrical panels. The PDM monitoring should be for the motor, gearbox and bearings; but that is another story.

Walt

Walt is ryt sam!!

I don't want to do a routine monitoring.Itz too risky and unsafe to stand beside the Motor & Gearbox when the crane moves over the furnace.

We have 2 cranes of same type, but in one of them some electronic components were failing frequently as i explained before. I don't know much about the components. They said it is Protection for IGBT(Transistor) and some resistors in the circuit get punctured frequently. The group formed for investigating these failures need to know the vibration levels of the panels.

My doubts are:

1.Can i do this with a general purpose accelerometer or i have to carry a slow speed sensor? (Don't say i have to use a seismic sensor,coz i have only these two. )

2.What type of setups to use? Do i need something special setup for this application?

Anyway thanks a lot guys.. Your comments were very useful!!

Surprise Sam!! I'm in Al-Jubail! I'm in Hadeed Steel Plant. Was there any special purpose for you to come here?

Have a nice time!!

Jenish, If you have 2 cranes and only one with problems I would compare the mount of the cabinets as there may be resonance problems that give so hi vibration levels that make components or soldering fatigue. For a basic survey I see no problem to start using what you have. If the major vibrations come from very lo freq. source it is a fair chance that the levels will be high enough for you to find with standard accels. Difference may also be if you have got wear marks in the tracks that differ between the cranes and that may be within normal freq. range at normal speed. So do a normal survey on the cabinet with what you normally use and see what you find. If you find nothing a measurement on the actual boards may need smaller accels but if this is for troubleshooting and not scientific looking at vibration isolation and tuning by adding weight may not be a bad idea. I isolated a switchgear container in a harbour crane once using normal vibration isolation devices as it could not survive living beside a vibro crusher. So hold on with one hand for your own safety and be careful. A knock test is never wrong either. Happy hunting. Olov

Get some baseline vibration readings on both cabinets, but I believe voltage spikes are what punctures transistors.

http://steiniche.dk/projekter/Komponenter/Transistor.htm